I'm just thinking once I get the hang of it, I'll go a bit farther and play around with music software. But it would be learn to read sheet music or use learning software to with the keyboard.are you going to be using the software to write sheet music or read it?
as far as the keyboard goes - 61 key is OK, especially if you are just playing around middle C. but once you start playing both hands further apart, 76 keys would be ideal. i know a guy who started to learn piano last year and a 61 unweighted key keyboard wasn't giving him all the keys he needed anymore. but it was a cheap way to see if he was interested in learning, and he recently upgraded to an 88 key weighted.
for learning, i've heard there are a number of good instructional channels on youtube.
I'm living in a small SRO apartment and a 61 keyboard will fit and I can move it at of way. I'm not so sure with 76 and 88 keys. I get a music keyboard for my birthday coming up.